Monovision (Blended Vision)
People approaching the age of 40–50 begin losing the ability to change visual focus from far to near. This causes a decrease in the ability to see clearly at near, when the eyes are adjusted for distance. Thus, if you naturally have clear distance vision, then you will begin to need “magnifying glasses” for clear close-up vision when you approach 40 – 50 years of age.
If your vision at distance is clear with glasses or contact lenses and you are 40-50 years of age, you will not see clearly at near with your glasses or contacts on unless they are bifocals, or unless one eye is purposefully under-adjusted. You will generally need bifocals for near vision, although some can remove their distance glasses and see well at near.
For people approaching or in this age group, we must decide how to best adjust your eyes given this change. People who use bifocals, reading glasses, or who need to remove their distance glasses for near vision usually understand this. However, people who have not yet crossed this threshold sometimes find this confusing.
People often refer to this condition mistakenly as “farsightedness”. To be accurate, it is not “farsightedness” at all. The medical term is “presbyopia”. This comes from Greek meaning “old eyes” (Since Dr. Caster is in this age group, we call it “middle-age eyes”). This is the aging condition of the eye that makes near vision difficult, whereas “farsightedness” is an inherent (not aging) difficulty with close-up vision. Unfortunately, there is no word in English other than “presbyopia” that describes this condition.
If you are nearsighted, farsighted, or have astigmatism and are developing presbyopia, you will probably need bifocal or trifocal glasses. The upper lenses of the bifocals are for distance vision; the lower are for close-up vision. Some people prefer trifocals, in which there are three pairs of lenses—an upper pair for distance, a middle pair for middle distances (about three to six feet), and a bottom pair for objects one to three feet away. Progressive lenses also have distance vision on the top and near vision at the bottom, but the tell-tale line between the different sections is eliminated.
Bifocal contact lenses are available but generally do not provide sharp vision for both distance and near.
For those of you approaching or in this age group, you and your doctor must decide how best to correct your vision when you develop presbyopia. This decision must be made regardless of how you choose to correct your refractive error—either surgically or with glasses or contact lenses. People who have already begun to use bifocals, trifocals, or reading glasses understand this. However, people who haven’t crossed this threshold yet or who simply remove their glasses when reading usually find this confusing.
“Honey, I think my arms are getting too short!”
You have three choices regarding your presbyopia. None of these options cure the presbyopia, so no option is ideal. Each has pros and cons. The key is to select the option that is most suitable for you.
1. Adjust for distance. Both eyes can be fully adjusted for clear distance vision. The patient will need to wear reading glasses (“magnifying glasses”) for good close vision, usually beginning sometime between the ages of forty and fifty. This might be referred to as the “normal” situation, because most people start to need reading glasses at about that age.
2. Blended vision. Blended vision, or monovision, adjusts one eye for distance and one for near vision for ideal focus. Blended vision is often created with contacts for people over forty-five and can be replicated with laser vision correction. The “distance” eye is used to see far objects, while the “close-up” eye is used to see near objects. Some blended vision patients will use glasses when driving a car or reading extensively. Other blended vision patients will almost never use glasses. Blended vision is achieved by purposefully leaving one eye somewhat nearsighted, either with contacts or laser treatment. Usually, this is the non-dominant eye (often the left eye in a right-handed person or the right in a left-handed person). If a patient chooses blended vision and doesn’t like it afterward, the “near” eye can usually be corrected in a second laser procedure. This will eliminate the remaining nearsightedness.
A person with both eyes corrected for distance can typically go back at a later date and have one eye readjusted for blended vision. Getting completely used to blended vision generally takes several weeks but may take several months, because you are breaking very well-established ways of using your eyes. People rarely ask to have blended vision eliminated after adjusting to it, but an enhancement procedure can accomplish this.
3. Mild Blended vision. This is a compromise between full distance vision in each eye and full blended vision. In mild blended vision, one eye is left with only a small amount of nearsightedness. This will cause a small decrease in distance vision in that eye, but will aid in mid-range and close-up vision. For many middle-aged patients, mild blended vision is a reasonable solution to poor distance vision combined with near vision loss. The degree of mild blended vision is adjustable, based on the patient’s age and visual demands. It can be further adjusted as the person ages.
Treatment at Caster Eye Center
How can you determine if full blended vision or mild blended vision might be right for you? During your consultation, Dr. Caster will show you blended vision using test glasses or contact lenses. Most people can immediately tell whether they like blended vision or not. If you desire a longer test period at home, you can request a pair of blended vision glasses or contacts.
A small number of people over forty with nearsightedness don’t wear bifocals, trifocals, or progressive glasses. These few exceptions merely take off their distance glasses when they want to read close-up. The key question you must ask yourself is: Can you read up close with your distance glasses on? If you must take off your distance glasses to read up close, then you have presbyopia. People with presbyopia who get both eyes corrected for distance vision will need to use reading glasses to see close-up. Some simply take off their glasses to read up close. If this is the case, you should carefully consider having laser treatment eliminating your distance glasses prescription.